Carbon transfer in the western South China Sea - biogeochemical perspectives on organic carbon pools in surface sediments, from source to burial

Abstract

Organic carbon (OC) entrainment, transmission and transformation along the terrestrialmarine continuum is fueled by terrestrial sources, modified by progressive in-situ mixing, production, and decomposition of marine OC. Bulk (OC, Nitrogen), molecular (Fatty acid methyl esters, FAME) and isotopic (δ 13Corg, Δ 14C) geochemical data are used in combination with mineral surface area and advanced computational models (Bayesian statistics, inversion models) to identify OC sources and their geochemical composition in estuarine and marine surface sediments of the South China Sea (SCS). A novel inversion modelling approach is presented that estimates OC pools (incl. petrogenic and dead carbon) validated against end-members. Dominance of marine OM is confirmed for coastal environments, implying efficient net loss of terrestrial OM, as it crosses the land-sea interface. The Δ 14C values range from modern to ~-970‰, with oldest OC focussed to the Red River outflow and remote regions of the Sunda Shelf palaeoriver systems, modern marine surface sediments are dominant in oceanic and shelf areas, which contrasts results from other studies from different river-marine shelf-open ocean systems available in the literature (e.g. the northern part of the SCS). Also reported, for the first time, anthropogenic synthetic organic compounds demonstrating the impact of potential pollution on the modern marine environment.